Radio communication systems are used for the transmission of information, speech or data, with the aid of electromagnetic waves over a radio interface between a sending and a receiving radio station. An example of a radio communication system is the known GSM mobile radio network, as well as its further development GPRS, for which the network architecture is described for example in B. Walke, “Mobilfunknetze und ihre Protokolls” (Mobile Radio Networks and their Protocols), Volume 1, Teubner-Verlag Stuttgart, 1998, Pages 139 to 151 and Pages 295 to 311. In this case a channel formed from a narrowband frequency range and a time slot is provided in each case for transmission of a subscriber signal.
For packet switched data transmission, the data is transmitted for a plurality of subscribers in the time division multiplex over one and the same channel. Each subscriber can thus occupy a plurality of channels simultaneously in this case.
For packet switching, a radio communication system, for example a GSM mobile radio network with GPRS, comprises a plurality of packet data service nodes (Serving GPRS Support Node, SGSN) which are internetworked and establish access to a fixed network. The Serving GPRS Support Nodes are further connected to Base Station Controllers (BSC). Each Base Station Controller in its turn makes possible at least one connection to at least one Base Station (BTS) and handles the administration of the technical resources of the base stations connected to it. Such a base station is a transceiver unit which can establish a telecommunication connection to mobile stations over a radio interface.
The individual subscribers are assigned to a channel via a packet data control unit which is provided in the base station controller in each case.
An area covered by a radio communication system is divided up into individual radio zones which are also referred to as cells. A cell here is served by one of the base stations via which radio connections are set up from mobile stations located in this cell. Further the area which is covered by a radio communication system is subdivided into residence zones, also known as routing areas. A routing area in this case comprises a plurality of radio cells. The area which is controlled by a Serving GPRS Support Node (SGSN) can be assigned a plurality of routing areas. The routing areas are administered by an administration system which is frequently also referred to as Mobility Management and is housed on the packet service node.
If a mobile station moves from the area of a cell into another cell, if the radio connection is still in place, an automatic procedure known as a handover is undertaken. This means that an active radio connection is retained even across cell borders. In the handover procedure the radio connection which is established over a first transceiver unit is switched over to a second transceiver unit.
If a mobile station moves out of the territory of one routing area into another routing area a process known as a routing area update must be undertaken. The mobile station is assigned an identifier in the relevant routing area, known in the GPRS system by the name of Temporary Logical Link Identifier (TLLI). In this case the mobile station must be assigned a new TLLI in the new routing area.
In the GPRS system, Release 5 (see 3GPP TS23.060, Pages 32 to 110) there is provision for the mobile station to establish the necessity for a handover procedure for packet switched data. If a handover procedure is to be performed for a mobile station, the mobile station registers with the base station of the new cell. If a change of routing area is taking place at the same time, a procedure for routing area update must first be performed, in which the mobile station will be assigned a new identifier. Only after the procedure for routing area update has successfully concluded can the exchange of data between the new transceiver unit and the mobile station continue. During the routing area update procedure the exchange of data is interrupted. This interruption is perceived as disruptive for various applications such as streaming applications or conversational services for example.